Radiotransmitter



D. ca. LITTLE RADIQ TRANSMITTER Filed April e, 1923 Dec. 15 1925' WITNESSES: INVENTOR Doha/d a. L/TH/e.

- V BY ATTORNEY Patentpd Dec. 15, 1925.

NITED STATES PATENT OFFICE.

DONALD G. LITTLE, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC & MANUFACTURING COMPANY, A. CORPORATION OF PENNSYL- VANIA.

RADIOTRANSMITTER.

Application filed April 6, 1928. Serial No. 630,266.

To all whom it may concern:

Be it known that I, DONALD G. Lrrr n, a citizen of the United States, and a resident of VVilkinsburg, in the county ofi Allegheny and State of Peimsylvania, have invented a new and useful Improvement in Radiotransmitters, of which the following is a specification.

My invention relates to wireless telegraphy, and, particularly, to wireless trans-- mlssion systems employing vacuum tubes as oscillation generators and as n'iodulators.

The principal object of my; invention isto provide a wireless transmission system remhodying simple switching means operable to cause said system to function as a telegraph or as a telephone transmission system.

According to my invention, I provide a transmission system comprising a pair of vacuum tubes together with switching means for causing one vacuum tube to function as an oscillator and the other vacuum tube to function as a modulator, when it is desired to transmit telephone messages, and for causing said modulator tube to function as an oscillator tube, when it is desired to transmit telegraph messages.

I have also. found that if the circuit extending from the modulator grid to the modulator filament be so connected as to include a resistor, which is embodied in the plate-filament circuit of the modulator tube,

said modulator grid may be given a negative bias represented by the potential dropacross said resistor.

\Vith these and other objects and applications in view, my invention further consists in the combination and in the details of construction and arrangement and operation hereinafter described and claimed and illustrated in the accompanying drawing wherein,

The single figure is a diagrammatic view of a wireless transmission system embodying my invention,

In the drawing is shown one particular arrangement of circuits and apparatus to which my invention is applicable and it is to be expressly understood that my invention. in its broader aspects, is not to be limited to the system shown therein. A pair of repeater devices 1 and 2 comprise, respectively, plate elements 3 and 4, grid elements 5 and 6 and hot-cathode elements 7 and 8, the lat- -continuous supply of en'er ter being energized from an alternating-current source of energy (not shown) through a transformer 9.

The repeater devices 1 and 2 may be provided with a pair of power-supply circuits 10 and 11 comprising individual portions 12 and 13, respectively, and a common portion 14, the latter portion terminating at the mid point of the secondary winding of the transformer 9. The individual portions 12 and 13'- includeradio-frequency choke coils 15 and 15 and also the primary and secondary power-supply circuits and is shunted by a source 21 of direct-current energy, whereby the repeaterdevices 1 and 2 may be energized. The condenser 19 serves as a reservoir for the energy source 21, providing a at all times, regardless of variations in t e amounts of energy absorbed in the system.

The repeater device 1 may be caused to function as an oscillator tube by providin the same with a plate-filament circuit 22 an a grid-filament circuit 23. The plate-filament circuit 22 comprises a condenser 24 having a low impedance to currents of radio frequency, a movable contact element 25 and a co-acting stationary contact element 26 of .a switch mechanism 27 a conductor 28 extending from the stationary contact element 26 to an adjustable ta 29 of an inductance coil 31, a portion of t e inductance coil belween the tap 29 and a grounded tap 32 and a conductor 33 extending from the grounded tap 32 to the mid-point of the secondary winding of the filament transformer 9.

The grid-filament circuit 23 for the repeater device 1 comprises a grid-biasing condenser 34,- which is shunted by a grid leak device 35, a movable contact element 36 and a co-acting stationary contact element 37 of a switch mechanism 38, a conductor 3!) extending from the stationary contact. element 37 to an adjustable tap 41 on the inductance coil 31, a portion of the inductance coil 31 between the taps 41 and 32, and the filament return conductor 33.

The end of the coupling coil 31 opposite to that connected to the grounded tap 32 15 connected to an antenna 42 to provide an oscillatoryradiating circuit.

The controlling grid element (3 of the repeater device 2 is connected to the hot cathode element 8 thereof through a movable contact element 43 and a co-acting stationary contact element 44 of a switch 45, a secondary winding 46 of a modulating transformer 47, the primary winding 48, of which is included in a .circuit comprising, in addition, a source 4!) of dirtwt-current energy and a transmitter 51 of the microphone type, a portion 52 of a resistor 58, which is serially included in the common portion 14 of the power supply circuits 10 and 11, the common portion 14 and the secondary winding of the lilament transformer 9.

The resistance of the resistor portion 52, which is. included in the grid-filament circuit of the repeater device 2, is such that, with normal currents tra\-ersing the common portion 14 of the power-supply circuits 10 and ll, the grid element (5 is maintained at a desired average negative bias.

In operation, when energy is supplied to the oscillator tube 1- from the energy source 21 through the power suppply circuit 10, high-frequency oscillations are generated in the plate circuit 22 and in the antenna 42 in accordance with well-known principles.

When voice waves are caused to enter the transmitter 51, variable potentials are impressed upon the controlling grid 6 of the modulator tube 2 tending to vary the impedance of the space-current path between the filament 8 and the plate 4. The effect of such variations is to causecorresponding variations in the currents traversing the plate-filament or so-called power supply circuit 11 of the modulator tube 2. The effect of such variations in the power-supply circuit 11 is to cause the introduction of corresponding potential variations in the power supply circuit 10 of the oscillator tube 1 through the coupled relation of the primary and secondary windings 16 and 17, respectively, of the coupling transformer 18. The resulting audio-frequency fluctuations in voltage across the late, filament elements 3 and 7,.respective y, is to cause the oscillatory currents generated by the tube 1 to be corres ondingly modulated. Thus, the ener radiated from the antenna 42 is modulate in accordance with sound waves impressed upon the telephone transmitter 51.

In order to cause the system just described to function as a continuous-wave telephone system, the following changes and additions are necessary. The plate elements 3 and 4 are connected to the stationary and movable contact elements 54 and 55, respectively, of a switch mechanism 56. The switch mechanism 45 is provided with an additional stationary contact element 57 designed to co-operate with the movable contact element 43, whereby the grid elements 5 and 6 may be connected in parallel relation. A circuit interrupting device 57 is connected in series circuit relation to the commonportion 14 of the power-supply circuits 10 and ll, whereby the power-supply to the tubes may be interrupted by the operation thereof. A condenser 58 may be shunted around said circuit interrupting device 57 to minimize the sparking at the operating contacts thereof.

The switch 27 is provided with an additional stationary contact member 58 providing a diti'erent connection for the plate elements to the inductance coil 31. Sinularly, the switch 38 is provided with an additional stationary contact element 5!) to provide a ditl'erentconnection for the grid e ements to the inductance coil 31. The ion-,- going additional stationary contact; members 58and 59 are employed when the transmission system is changed from telephone operation to telegraph operation, as will appear more fully hereafter. The several switches may be interconnected by a common handle member 61, whereby the same may be operated in unison.

When the several switches are moved from the position shown in the drawing to engage, respectively, the stationary contact. elements 54, 57, 58 and 59, the repeater devices l and 2 are connected in parallel relation, thereby changing the function of the modulator tube 2 to that of an oscillator tube. Signaling may now be accomplished by the operation of the cireuit-interrupnng device 57, since the closin r and the opening of the same connects and isolates the energy source 21 from the elements of said tubes.

lVhen the transformer windings 16 and 17 are wound in the same direction, the inductive etl'ec-t thereof is to introduce a time lag for current changes which is of such magnitude that the control of the tubes through the closing and the opening of the common portion 14 ofthe power-supply circuits is impossible.

The foregoing difliculty is obviated in my invention by oppositely arranging the transformer windings 16 and 17, whereby with equal currents traversing each winding, the inductive impedance of the transformer, as a whole, is substantially zero.

While I have shown only one embodiment of my invention, for the purpose of describing the same and illustrating its principle of operation, it is susceptible of various chan es and modifications without de arting trom the spirit thereof, I desire, t erefore, that only such limitations shall be imposed thereon, as are indicated by the appended claims or are demanded by the prior art.

I claim as my invention:

1. A pair of tubes provided with plate circuits including transformer windings, said plate circuits being interlinked through said transformer windings, means for, at will connecting said tubes in parallel and means included in one of said plate circuits for controlling the parallel operation of said tubes.

2. A pair of space-current devices provided with power-supply circuits, a coupling transformer having a winding individual to each circuit, means for, at will, connecting said devices alternatively in parallel relation or in another operative reation, and circuit interrupting means included in said power supply circuits for controlling the operation of said devices when connected in parallel, said transformer having a negligible inductive impedance when said devi-es are operating in parallel.

3. A pair or space-current devices .provided with power-supply circuits having corresponding individual portions and a common portion, a transformer having windings in said individual portions, a source of energy for said devices and circuit interrupting means serially included in said common. portion, and switchin means for connecting said devices in aral el, said transformer having a negligib e impedance for said parallel connection.

4. In an electrical system, the combination with an oscillator tube having a powersupply circuit, of a modulator tube also having a power-supply circuit, said modulator tube having a grid-filament circuit in cluding a modulating device and a ortion of said modulator-tube power-supp y circuit, said portion including a grid biasing device.

5. In an electrical system, the combinetion with an oscillator tube having a grid element and provided with a power-supply circuit, of a modulator tube having a grid element and provided with a power-supply circuit, and a grid-filament circuit including a modulating device and deriving energy from said modulator-tube owersupply circuit for biasing said mo ulator tube grid element, said power-supply circuits having individual portions and a common portion, a transformer having wind ings in the ndividual portions, a source of energy and circuit interrupting means in-= eluded in the common portion and switching means for changing the function of said modulator tube to that of an oscillator tube cooperating with said first-mentioned tube, said transformer having a negligible impedance for said parallel connection of tubes.

6. In a radio sending system, a vacuum tube oscillator, a vacuum tube modulator, a grid biasing means for the modulator located in the plate-circuit thereof, switch ing means for converting said modulator into a vacuum tube oscillator connected in parallel with the first named vacuum tube oscillator, and a signal-producing circuitcontrolling device in the plate circuit of said arallel oscillators between said grid biasmg device and the cathodes.

7. In a radio sending system, a vacuum tube oscillator, a vacuum tube modulator, a grid biasing means for the modulator located in the plate circuit thereof, switching means for converting said modulator into a vacuum tube oscillator connected in parallel with the first named vacuum tube oscillator, and a signal-producing circuitcontrolling device in the plate circuit' of said parallel oscillators between said grid biasing device and the cathodes, the grid circuit of the last named oscillator being completed outside of said grid biasing de-' v1ce.

In testimony whereof, I have hereunto subscribed my name this 15th day of March, 1923.

DONALD G. LITTLE. 

